Reflector with a resistant surface

Stock material or miscellaneous articles – Composite – Of metal

Reexamination Certificate

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C428S448000, C428S450000, C428S458000, C428S650000, C428S654000, C428S701000, C428S702000, C428S908800, C428S699000, C427S163100

Reexamination Certificate

active

06670045

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a reflector with high total reflection, resisting mechanical stress and comprising a reflector body of metal and arranged thereon superimposed,
BACKGROUND ART
a) a functional coating, made of a gel-film, lacquer or polymer of thickness 0.5 to 20 &mgr;m or, in the case of a reflector body of aluminium, also of anodically oxidised aluminium formed directly out of the aluminium lying on the surface of the reflector body, of thickness 10 to 1500 nm, and
b) a reflection layer structure composed of a reflecting layer and a plurality of transparent layers.
The invention also concerns the use of such reflectors.
It is generally known to produce strips of highly reflective materials such as e.g. high purity aluminium or AlMg alloys based on aluminium with a purity level of 99% and higher, such as e.g. 99.5%, and to produce roll surfaces that create diffuse or directional reflection, depend-ing on the application. It is also known, in order to increase the directional reflection (degree of reflection), to brighten the surfaces of such strips chemically or electrolytically and sub-sequently to provide them with a protective, e.g. 1.5 &mgr;m thick layer by anodic oxidation.
The known processes have the further disadvantage that high purity and expensive alloys based on high purity aluminium have to be employed. The anodic oxide layer causes the degree of reflection to be lowered and, as a result, both the total reflection and the directional reflection, due to absorption and diffuse light scattering, in particular in the oxide layer. This represents a loss of energy.
Known from EP-A-0 495 755 are items with surfaces of aluminium which are suitable for depositing layer systems from the gas phase onto these surfaces. Anodising the surface is dispensed with and a layer system is described comprising e.g. an adhesive layer, such as a ceramic layer, a light reflecting layer, such as a metallic layer e.g. of aluminium and one or more transparent protective layers e.g. of the oxides, nitrides or fluorides of magnesium, titanium or praseodymium. Such layer systems exhibit a high degree of reflection. Such a layer system, however, has the disadvantage of being very sensitive to mechanical effects.
BROAD DESCRIPTION OF THE INVENTION
EP-A-0 586 943 describes the precipitation of a reflection layer which is based on aluminium and superimposed on this a gel film that has been deposited on the aluminium by a sol-gel process. The reflection is achieved by a layer system comprising layers of silicon oxide, metal, silicon dioxide and titanium dioxide. This is also a possibility for achieving reflecting aluminium-based materials. The layer structure described in EP-A 0 568 943 is not resistant to mechanical stress to the desired degree.
The document WO 97/01775 describes bent reflectors with a reflector body of glass and provided thereon a primary layer of silicon or silicon and stainless steel and, situated on top of that, a reflecting metal layer which is covered by a protective layer e.g. of silicon-nitrite.
Known from EP-A-O 456 488 are reflectors having a foundation and a reflecting layer provided thereon and a subsequent layer system comprising high and low refractive index layers, where the reflecting layer is deposited directly on the substrate or on a dielectric layer. The layer system may be covered by a protective layer.
The object of the present invention is to avoid the above mentioned disadvantages and to propose reflectors with outer layers that are insensitive to external mechanical stress and are characterised by a high resistance to wiping.
That objective is achieved by way of the invention in that the reflection layer structure comprises a silicon oxide of general formula SiO
x
where x represents a number from 1.1. to 2.0, or aluminium oxide having the formula Al
2
O
3
, of thickness 3 nm (nanometre) or more as protective layer and the protective layer as the layer lying on the surface protects the under-lying layers against mechanical damage and the protective layer exhibits no surface damage in the wipe test according to DIN 58196 after 50 test cycles each of 100 wiping strokes.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention the protective layer basically belongs to the transparent layers within the structure of reflection layers.
In one useful version the minimum thickness of the protective layer amounts to 3 nm. The maximum thickness of the protective layer may e.g. be 1000 nm, advantageously 400 nm. In another version the thickness of the protective layer is preferably 40 nm or less. In particular the thickness of the protective layer is 3 to 20 nm. In the present description of the invention the letters nm stand for nanometre.
In a further version the thickness of the protective layer can also be defined by its optical thickness (or depth). The optical thickness is preferably described by the formula n·d=&lgr;/2±40 nm. The optical thickness may also be a multiple thereof expressed by k, where k is a natural number such as 2, 3, 4, 5, 6. 7, 8, 9 or 10. In this formula n stands for the index of refraction and d the geometric thickness. The symbol &lgr; stands for the intensity maximum of the wave lengths of the reflected electromagnetic radiation. In the case of visible light &lgr; lies in the region of approximately 550 nm.
The reflecting body in question may be any three-dimensional object having at least one free surface of a metal, such as iron, steel, aluminium or aluminium alloy. These free surfaces may be an aluminium with a purity of 98.3% and higher in certain cases with a purity of for example 99.0% and higher, 99.7% and higher, 99.9% and higher or 99.95% and higher. Apart from aluminium of the above mentioned purities the surface may also be of an alloy. Preferred alloys are those belonging to the AA 1000, AA 3000 and AA 5000 series. Further preferred alloys contain e.g. 0.25 to 5 wt. % magnesium, in particular 0.5 to 4 wt. % magnesium, or 0.2 to 2 wt. % manganese, or 0.5 to 5 wt. % magnesium and 0.2 to 2 wt. % manganese, in particular e.g. 1 wt. % magnesium and 0.5 wt. % manganese, or contain 0.1 to 12 wt. % copper, preferably 0.1 to 5 wt. % copper, or contain 0.5 to 6 wt. % zinc and 0.5 to 5 wt. % magnesium, or contain 0.5 to 6 wt. % zinc, 0.5 to 5 wt. % magnesium and 0.5 to 5 wt,% copper, or contain 0.5 to 2 wt. % iron and 0.2 to 2 wt. % manganese, in particular e.g. 1.5 wt. % iron and 0.4 wt. % manganese or AlMgSi alloys or AlFeSi alloys. Further examples are AlMgCu alloys such as A199.85Mg0.8Cu or AlMg alloys such as AlMg1.
Especially preferred free surfaces are e.g. of aluminium having a purity of 99.5 % and higher, 99.8% and higher, 99.85% and higher or surfaces of an aluminium alloy containing 0.5 wt. % magnesium or containing 1 wt. % magnesium, or containing aluminium having a purity of 99% and 5 to 10 wt % magnesium, in particular 7 wt. % magnesium and 6 to 12 wt. % copper, in particular 8 wt. % copper. Especially preferred are also all aluminium alloys that can be rolled.
Examples of reflector bodies are castings and forgings and, in particular, rolled products such as foils, strips, plates, sheets that may be shape-formed by bending, deep-drawing, cold impact extrusion and the like. Further, extrusions, beams or other shapes may be employed.
Depending on the application in question, the whole reflector body may be made of metal, preferably of the above mentioned aluminium or aluminium alloy; it is possible for only parts or only parts of the surface area to be of metal.
The above mentioned metal and in particular the aluminium or aluminium alloy may also be part or a part of a surface of a composite e.g. a laminated foil or laminates of any material of choice such as e.g. plastics or and metals such as Al-coated steel sheet or Al-coated plastic.
The aluminium surfaces may also be subjected to a chemical or electrochemical process or an alkaline pickling process. Such brightening or pickling processes are employed prior to anodising.
The aluminium surfaces may, for any topograph

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